1. Field of the Invention
The present invention relates to a tone-conversion device for image, program, an electronic camera, and a method thereof.
2. Description of the Related Art
U.S. patent Publication No. 20030156761 (hereinafter, referred to as Patent document 1) discloses a method of compressing a dynamic range by the following equation:O[i, j]=I[i, j]×F(R[i, j]) . . . [100]where I[i, j] is a pixel value of an input image, O[i, j] is a pixel value of an output image, F( ) is a coefficient calculation function, and R[i, j] is a pixel value of the input image subjected to epsilon filtering. The epsilon filter is a nonlinear filter which nonlinearly extracts a small amplitude component from the input image and subtracts the small amplitude component from the input image.
The processing with the epsilon filter according to the Patent document 1 is complicated and time-consuming which causes a problem. On the other hand, the use of a simple low pass filter instead of the epsilon filter causes another problem of occurrence of a halo in a portion with a great luminance difference.